1. Field of the Invention
This invention relates to an integrated process for thermochemically transforming biomass into high quality liquid fuels. As used herein, the term “biomass” refers to biological material derived from living or deceased organisms and includes lignocellulosic materials, such as wood, aquatic materials, such as algae, aquatic plants, seaweed, and animal by-products and wastes, such as offal, fats, and sewage sludge. In one aspect, this invention relates to a substantially self-sustaining process for creating high quality liquid fuels from biomass. In another aspect, this invention relates to a multi-stage hydropyrolysis process for creating high quality liquid fuels from biomass. In another aspect, this invention relates to a hydropyrolysis process for transforming biomass into high quality liquid fuels in which all of the process fluids are provided by the biomass. In another aspect, this invention relates to a hydropyrolysis process for transforming biomass into high quality liquid fuels in which the process outputs are substantially only liquid product and CO2. In another aspect, this invention relates to an integrated process for producing gasoline and diesel fuels from biomass using a hydrocracking catalyst.
2. Description of Related Art
Conventional pyrolysis of biomass, typically fast pyrolysis, does not utilize or require H2 or catalysts and produces a dense, acidic, reactive liquid product that contains water, oils, and char formed during the process. Because fast pyrolysis is most typically carried out in an inert atmosphere, much of the oxygen present in biomass is carried over into the oils produced in pyrolysis, which increases their chemical reactivity. The unstable liquids produced by conventional pyrolysis tend to thicken over time and can also react to a point where hydrophilic and hydrophobic phases form. Dilution of pyrolysis liquids with methanol or other alcohols has been shown to reduce the activity and viscosity of the oils, but this approach is not considered to be practical or economically viable, because large amounts of unrecoverable alcohol would be required to produce and transport large amounts of pyrolysis liquids.
In conventional pyrolysis carried out in an inert environment, the water miscible liquid product is highly oxygenated and reactive, with total acid numbers (TAN) in the range of 100-200, has low chemical stability for polymerization, is incompatible with petroleum hydrocarbons due to water miscibility and very high oxygen content, on the order of about 40% by weight, and has a low heating value. As a result, transport and utilization of this product are problematic and it is difficult to upgrade this product to a liquid fuel due to the retrograde reactions that typically occur in conventional pyrolysis and in conventional fast pyrolysis. In addition, the removal of char generated by conventional pyrolysis from the liquid pyrolysis product presents a technical challenge due to the large amounts of oxygen and free radicals in the pyrolysis vapors which remain highly reactive and form a pitch-like material when they come in intimate contact with char particles on the surface of a filter. Consequently, filters used to separate the char from the hot pyrolysis vapors blind quickly due to the reactions of char and oil that occur on and within the layer of char on the surface of the filter.
The upgrading of pyrolysis oils produced by conventional fast pyrolysis through hydroconversion consumes large quantities of H2, and extreme process conditions make it uneconomical. The reactions are inherently out of balance in that, due to the high pressures required, too much water is created while too much H2 is consumed. In addition, hydroconversion reactors often plug due to coke precursors present in the pyrolysis oils or from coke produced as a result of catalysis.
In general, hydropyrolysis is a catalytic pyrolysis process carried out in the presence of molecular hydrogen. Typically, the objective of conventional hydropyrolysis processes has been to maximize liquid yield in a single step. However, in one known case, a second stage reaction was added, the objective of which was to maximize yield while maintaining high oxygen removal. However, even this approach compromises economy, creates a system which requires an external source of H2, and must be carried out at excessive internal pressures. In addition to requiring a continuous input of hydrogen, such conventional hydropyrolysis processes produce excessive H2O which must then be disposed of.